The present invention relates to an arrangement and a method for adapting a cruise control system of a vehicle. The invention further relates to a computer program adapted to perform such a method in a cruise control system when said program is run on a computer, and a computer program product comprising such program code means stored on a computer readable medium. The arrangement is suitable gear vehicles of different kinds which are provided with economy driving settings.
Modern vehicles are often provided with a cruise control system in order to improve the comfort of a driver. Some cruise control system are provided with further functions, such as an adaptive control system that uses distance measuring equipment to monitor the distance to a vehicle in front of the own vehicle, in order to be able to adapt the cruise speed to the speed of the vehicle in front. Such a system will improve the safety of the cruise control system since a minimum distance to the vehicle in front will be maintained. Some systems will also brake the vehicle if the minimum distance is not maintained, or if the distance to the vehicle in front decreases at a certain rate. The cruise control system may be adapted to maintain a set speed by using only the accelerator, or by also using the brakes of the vehicle. This is especially common in heavy vehicles which are equipped with auxiliary brakes, such as engine brakes and retarders. A further function of the cruise control system of the vehicle may be an economy dove setting, in which the regulating parameters of cruise control system are ruled by economy.
The cruise control system has a regulating range in which the actual speed value is maintained. For a system using only the accelerator to maintain the speed, an excessive speed of a few percent may be allowed. Typically, the speed ma in this case vary between e.g. 68 to 72 when the speed is set to 70 km/h. It may be possible to set the maximal allowed excessive speed value for the vehicle. In this way, the system can allow the vehicle to travel at an excessive speed at certain occasions, e.g. when travelling on a slight descent.
When the brake system is also used to maintain the speed of the vehicle, referred to as a brake cruise system, a specified excessive speed can also be allowed for a vehicle rolling down a fairly steep downhill slope. An allowed excessive speed may help to preserve energy by using the momentum of the vehicle. The limit for the allowed excessive speed must of course be set to a value that does not endanger other vehicles.
There are however situations in which the traditional regulating method of the cruise control system does not work in a fuel efficient way. Such situations may e.g. be when the vehicle travels in ascents and descents or when a sudden change in pace is required. In an ascent, a cruise control system of the kind mentioned above will try to maintain a speed of 68 km/h regardless of the steepness of the ascent. This may lead to the vehicle travelling up an ascent with full throttle. In the same way, the speed of the vehicle travelling down a descent is maintained at 72 km/h by engaging the brakes.
There is thus a need for an improved cruise control system that is more energy efficient.
It is desirable to provide an improved cruise control arrangement for a vehicle, where the cruise control operation is adapted to an economy setting. It is also desirable to provide an improved method for adapting the operation of a cruise control system of a vehicle.
In a cruise control arrangement for a vehicle, where the cruise control arrangement is provided with a cruise control speed function, a cruise control brake function and at least one selectable economy level, where the arrangement has a set maximum speed value corresponding to a maximum allowed vehicle speed, a set brake speed value corresponding to a brake cruise speed and a set cruise speed value corresponding to a cruise speed, the problem is solved in that a temporary brake speed value replaces the set brake speed value as the actually used brake speed value when an economy level is selected, where the temporary brake speed value is dependent on the selected economy level.
By this first embodiment of the cruise control arrangement, the arrangement replaces the set brake speed value with a temporary brake speed value depending on a selected economy level. The set brake speed value is kept, and the temporary brake speed value is used as the actual brake speed value as long as the selected economy level is selected. If another economy level is selected, a new temporary brake speed value will be used depending on the selected economy level. If the economy function is switched off, the set brake speed value will be used again as the actual brake speed value. In this embodiment, a cruise control function that is more energy efficient is obtained, in that the allowed speed offset from the set cruise speed is adapted in dependence of the selected economy level. By selecting an economy level, a greater difference between the set cruise speed and the used brake speed is obtained, as compared with no economy level. For a system having several economy levels, the selection of a higher economy level will generate an even greater difference between the set cruise speed and the used brake speed. A greater speed difference between the set cruise speed and the used brake speed will allow the vehicle to preserve more momentum when travelling down a hill, which will save fuel. The set brake speed value is kept as the default brake speed value. The set brake speed value is used together with an offset speed value corresponding to the selected economy level to obtain the temporary brake speed value.
In an advantageous development of the inventive arrangement, the temporary brake speed value is not allowed to be greater than the set maximum speed value. If the sum of the set brake speed value and the offset speed value is equal or larger than the set maximum speed value, the temporary brake speed value is set equal to the set maximum speed value. In this way, it is guaranteed that the maximum speed of the vehicle is held within the predefined limits.
In an advantageous development of the inventive arrangement, the set cruise speed value can also be replaced with a temporary cruise speed value. The temporary cruise speed value is dependent on the selected economy level and the temporary brake speed value. Since the temporary brake speed value gives a larger difference between the used brake speed value and the set cruise speed value, it may be necessary to replace the set cruise speed value with a temporary cruise speed value in order to obtain the desired difference between the used brake speed value and the used cruise speed value. This is the case when the temporary brake speed value is set equal to the set maximum speed value. In this case, the temporary cruise control speed is selected such that the speed interval between the temporary cruise control speed and the set maximum speed value is the same as the speed interval between the set cruise control speed and the sum of the set brake speed value and the offset speed value.
In an advantageous development of the inventive arrangement, the temporary cruise speed value is used as the actual cruise speed value until the economy level is changed to a level where the speed interval between the set maximum speed value and the temporary cruise speed value corresponds to the speed interval between the set cruise speed value and the offset speed value added to the set brake speed value. Further, the set cruise speed value is used as the actual cruise speed value when the speed interval between the set maximum speed value and the set cruise speed value is smaller than the speed interval between the set cruise speed value and the offset speed value added to the set brake speed value. In this way, the original settings of the cruise control systems remains untouched and can be used by the driver when the economy level is switched off without having to re-enter the settings again. This will enhance the safety of the system since the driver is not exposed to any surprises when it comes to the cruise control settings.
In a method for changing the reference brake speed value in a cruise control arrangement for a vehicle comprising a cruise control speed function, a cruise control brake function and at least one selectable economy level, having a set maximum speed value, a set brake speed value and a set cruise speed value, the steps of adding an offset speed value corresponding to a selected economy level to the set brake speed value and using the sun of the offset speed value and the set brake speed value as a temporary brake speed value are comprised.
With the inventive method, an optimized behaviour of the cruise control system of a vehicle can be obtained, in which the cruise control system is adapted to the road characteristics. In this way, the fuel consumption can be lowered compared with a cruise control using nominal set parameters to regulate the operation of the vehicle.